The ranking takes into account four factors. First, we measured how many people a person has power over. For a religious leader, like Pope Benedict XVI (#7), that would be the number of adherents, or Catholics, in the world. For a CEO, like General Electric’s Jeffrey Immelt (#28) we counted the number of employees.

Then we looked at the financial resources controlled by each candidate, whether that is revenues (for a company), GDP (for a country) or net worth (for a billionaire). Next we asked: Is a candidate influential in more than one arena, or sphere? This bumped up the ranking of people like New York City Mayor Michael Bloomberg (#17), who is a powerful politician, a self-made media billionaire and a major philanthropist.

Finally, we gave consideration to how actively the candidates wield their power. This measure eliminated inactive heirs to great fortunes, semi-retired industrialists and former heads of state. In all, 70 people made the final list, one for every 100 million people on the planet.

Regaining the title of the World’s Most Powerful Man on this year’s list is President Barack Obama, who gave up the top spot last year to China’s president Hu Jintao (#3). Despite his current political weakness, Obama remains the head-of-state of the world’s largest, most dynamic economy, commander-in-chief of the planet’s deadliest military and, unofficially, the leader of the free world. Moreover, Hu’s relative power is decreasing as he starts giving up important political offices, including general secretary of the Chinese Communist Party, to his successor Xi Jinping (#69).

In second place is Russian prime minister Vladimir Putin, who is poised to regain the Russian presidency this year from his loyal underling president Dmitry Medvedev (#59). German chancellor Angela Merkel ranks fourth and rounding out the top five is Bill Gates, co-chair of the world’s largest charity, chairman of Microsoft and America’s richest man.

Facebook CEO Mark Zuckerberg (#9) is the youngest person on the list at age 27, and the biggest gainer this year, jumping 31 spots from 40th in 2010. Also moving up is Jeff Bezos, the CEO of Amazon, who ranks 40th, 26 spots higher than last year. Bezos, who is already the largest “e-tailer” on Earth, is now exerting increasing power over the publishing business through the Kindle and Amazon Web Services powers some the biggest sites, including Zynga and Netflix.

On the flip side, Tenzin Gyatso, the 14th Dalai Lama, fell twelve spots this year to 51st after announcing that he plans to give up his position atop Tibet’s government in exile. The world’s arbiter of good taste, luxury purveyor Bernard Arnault (#65) of LVMH also took a tumble in the rankings, falling from 43rd in 2010.

Two criminals made this year’s list. Joaquin Guzman Loera (#55), the billionaire head of the Sinaloa drug cartel, that operates with seeming immunity in Northern Mexico and Dawood Ibrahim Kaskar (#57), who heads an organized crime syndicate in Mumbai and is suspected of providing logistical and financial support for terrorists.

Life is not easy at the top. Ten people fell off the list this year due to declining influence, including Oprah Winfrey, disgraced French politician Dominique Strauss-Kahn and former Japanese prime minister Naoto Kan. Others departed in a more definitive way, including Apple cofounder Steve Jobs (Feb. 24, 1955 – Oct. 5, 2011) and Osama bin Laden (Mar. 10, 1947 – May 2, 2011).